End cap seal for an electrochemical cell

ABSTRACT

An end cap seal assembly for an electrochemical cell such as an alkaline cell is disclosed. The end cap assembly comprises a metal support disk and underlying insulating sealing disk and a metal end cap overlying the metal support disk. The edge of the end cap and metal support disk is captured by the crimped edge of the insulating sealing disk. The support disk has a downwardly extending wall with at least one aperture therethrough. The insulating disk is preferably composed of a polyetherurethane material and may have a slanted downwardly extending wall forming a rupturable membrane which underlies and abuts the inside surface of the downwardly extending wall of the support disk. A portion of the rupturable membrane underlies and abuts the aperture in the downwardly extending wall of the support disk. The rupturable membrane pushes through said aperture and ruptures when gas pressure within the cell exceeds a predetermined level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of application Ser. No.11/590,561, filed Oct. 31, 2006.

FIELD OF THE INVENTION

The invention relates to an end cap assembly for sealing electrochemicalcells, particularly alkaline cells. The invention relates to rupturabledevices within the end cap assembly which allow gas to escape from theinterior of the cell to the environment. The invention relates torupturable devices comprised of polyetherurethane material.

BACKGROUND

Conventional electrochemical cells, such as alkaline cells, are formedof a cylindrical housing having an open end and an end cap assemblyinserted therein to seal the housing. Conventional alkaline cellstypically comprise an anode comprising zinc, a cathode comprisingmanganese dioxide, and an alkaline electrolyte comprising aqueouspotassium hydroxide. After the cell contents are supplied, the cell isclosed by crimping the housing edge over the end cap assembly to providea tight seal for the cell. The end cap assembly comprises an exposed endcap which functions as a cell terminal and typically a plasticinsulating plug, which seals the open end of the cell housing. A problemassociated with design of various electrochemical cells, particularlyalkaline cells, is the tendency of the cell to produce gases as itcontinues to discharge beyond a certain point, normally near the pointof complete exhaustion of the cell's useful capacity.

Electrochemical cells, particularly alkaline cells, may be provided witha rupturable venting mechanism which includes a rupturable diaphragm orrupturable membrane within an end cap assembly. The rupturable diaphragmor membrane may be formed within a plastic insulating member asdescribed, for example, in U.S. Pat. No. 3,617,386. Such diaphragms aredesigned to rupture when gas pressure within the cell exceeds apredetermined level. The end cap assembly may be provided with ventholes for the gas to escape when the diaphragm or membrane is ruptured.The end cap assembly disclosed in U.S. Pat. No. 3,617,386 discloses agrooved rupturable seal diaphragm and a separate metal contact diskbetween the end cap and seal diaphragm. The end cap assembly disclosedin the reference is not designed to withstand radial compressive forcesand will tend to leak when the cell is subjected to extremes in hot andcold climate.

In order to provide a tight seal contemporary prior art disclose end capassemblies which include a metal support disk inserted between the endcap plate and an insulating member. The separate metal support disk maybe radially compressed when the cell housing edge is crimped over theend cap assembly. The insulating plug is typically in the form of aplastic insulating disk which extends from the center of the celltowards the cell housing and electrically insulates the metal supportdisk from the cell housing. The metal support disk may have a highlyconvoluted surface as shown in U.S. Pat. Nos. 5,759,713 or 5,080,985which assures that the end cap assembly can withstand high radialcompressive forces during crimping of the cell's housing edge around theend cap assembly. This results in a tight mechanical seal around the endcap assembly at all times.

The prior art discloses rupturable vent membranes which are integrallyformed as thinned areas within the insulating disk included within theend cap assembly. Such vent membranes are normally oriented such thatthey lie in a plane perpendicular to the cell's longitudinal axis, forexample, as shown in U.S. Pat. No. 5,589,293. In U.S. Pat. No. 4,227,701the rupturable membrane is formed of an annular “slit or groove” locatedin an arm of the insulating disk which is slanted in relation to thecell's longitudinal axis. The insulating disk is slideably mounted on anelongated current collector running therethrough. As gas pressure withinthe cells builds up the center portion of the insulating disk slidesupwards towards the cell end cap, thereby stretching the thinnedmembrane “groove” until it ruptures. U.S. Pat. Nos. 6,127,062 and6,887,614 B2 disclose an insulating sealing disk and an integrallyformed rupturable membrane therein which is inclined. The rupturablemembrane portion in the sealing disk abuts an aperture in the overlyingmetal support disk. When the gas pressure within the cell rises themembrane ruptures through the aperture in the metal support disk therebyreleasing the gas pressure which passes to the external environment.

In U.S. Pat. No. 6,887,614 the rupturable membrane abuts an opening inan overlying metal support disk. In U.S. Pat. No. 6,887,614 there is anundercut groove on the underside of the membrane. The groove circumventsthe cell's longitudinal axis. The groove creates a thinned membraneportion at its base which ruptures through the opening in the overlyingmetal support disk when the cell's internal gas pressure reaches apredetermined level. In the design shown in U.S. Pat. No. 6,887,614there is an insulating washer which separates the exposed end cap fromthe cell housing. Such design has the disadvantage of requiring anadditional component, namely, the insulating washer which needs to beinserted into the end cap assembly. The edge of the end cap sits overthe cell housing shoulder and is separated from the housing by thewasher. This allows for tampering of the end cap, that is, the end capmay be readily pried away from the cell allowing easier access to thecell contents.

The rupturable membrane can be in the form of one or more “islands” ofthin material within the insulating sealing disk as shown in U.S. Pat.No. 4,537,841; U.S. U.S. Pat. No. 5,589,293; and U.S. Pat. No.6,042,967. Alternatively, the rupturable membrane can be in the form ofa thin portion circumventing the cell's longitudinal axis as shown inU.S. Pat. No. 5,080,985 and U.S. Pat. No. 6,991,872. The circumventingthinned portion forming the rupturable membrane can be in the form ofslits or grooves within the insulating disk as shown in U.S. Pat. No.4,237,203 and U.S. Pat. No. 6,991,872. The rupturable membrane may alsobe a separate piece of polymeric film which is sandwiched between themetal support disk and the insulating disk and facing apertures thereinas shown in Patent Application Publication US 2002/0127470 A1. A pointedor other protruding member can be oriented above the rupturable membraneto assist in rupture of the membrane as shown in U.S. Pat. No.3,314,824. When gas pressure within the cell becomes excessive, themembrane expands and ruptures upon contact with the pointed member,thereby allowing gas from within the cell to escape to the environmentthrough apertures in the overlying terminal end cap.

A separate metal support disk, typically with convoluted surfaces asshown in U.S. Pat. Nos. 5,080,985 and 5,759,713, has been includedwithin the end cap assembly. The metal support disk provides support forthe plastic insulating seal and withstands high radial compressiveforces which may be applied to the end cap assembly during crimping ofthe housing edge around the end cap assembly. The high radialcompressive force assures that the seal along the peripheral edge of theend cap assembly and cell housing can be maintained even if gas pressurewithin the cell builds up to high level, for example, over 1000 psig(689.4×10⁴ pascal gage).

In U.S. Pat. No. 4,537,841 is shown a plastic insulating sealing plug ordisk for closing the open end of a cylindrical alkaline cell. There is ametal support disk over the insulating seal. The plastic insulating sealhas a central hub and integrally formed radial arm which extendsradially from the hub to the cell's casing wall. An “island” typerupturable membrane is formed integrally within the radially extendingarm of the insulating seal. The “island” rupturable membrane is formedby stamping or compressing a portion of the radially extending arm ofthe insulating seal thereby forming a small circular thinned islandportion, which is designed to rupture when gas pressure within the cellreaches a predetermined level. The island rupturable membrane shown inthis reference is level with the radially extending arm of theinsulating seal, that is, it is oriented in a plane perpendicular to thecell's central longitudinal axis. The top surface of the thinnedrupturable membrane (facing the cell's open end) is very nearly levelwith the top surface of the radially extending insulating arm. Thisdesign while effective provides only a small limited space between therupturable membrane and the metal support disk. When the cell issubjected to intentionally abusive conditions such as exposure to fire,this may result in very quick rise in cell internal temperature andgassing. It is possible under such extreme condition that the membranemay “balloon” out without rupturing because the membrane softens andthere is only a small space between the membrane and the metal supportdisk.

In view of improvements in gassing inhibitors and in particular the useof multiple gassing inhibitors, modern alkaline cells can be designed tovent at somewhat lower pressures than in the past. That is, there hasbeen a trend towards lowering the design activation pressures forventing mechanisms in alkaline cells. Lower design vent activationpressures poses design challenges. If an “island” type rupturablemembrane is used to trigger the venting mechanism, there are practicallimitations as to how thin such membrane can be molded usingconventional molding techniques such as injection molding. Also thereare limitations on the amount of surface area available for suchmembranes depending on cell size. Also if conventional material such asnylon 66 is employed for the plastic insulating sealing plug it becomesmore difficult to mold the thinned rupturable membrane portion of suchmaterial to the very small thicknesses required to accomplish therupture at low pressure threshold. The small membrane thickness isrequired because of the high ultimate tensile strength of such material.

Accordingly, it is desirable to have an end cap assembly which providesa tight seal for the cell and resists leakage even though the cell maybe exposed to extremes in both hot and cold climate.

It is desired to have a reliable rupturable venting mechanism within theend cap assembly which activates and functions properly even when thecell is subjected to abusive conditions.

It is desirable that the end cap be tamper proof, that is, cannot bereadily pried from the end cap assembly.

It is desired that and rupturable venting mechanism be readilymanufactured and reliable so that venting occurs at a specificpredetermined pressure level.

SUMMARY OF THE INVENTION

The invention is directed to an electrochemical cell, for example analkaline cell, comprising an end cap seal assembly inserted into theopen end of a cylindrical housing (casing) for the cell. In one aspectthe end cap assembly comprises a metal support disk and an underlyinginsulating sealing plug (insulating sealing disk) underlying the metaldisk when the cell is viewed in vertical position with the metal supportdisk on top. The end cap assembly also comprises a terminal end cappositioned over the metal support disk.

The metal support disk is preferably formed of a disk of single piecemetallic construction having a convoluted surface and at least one ventaperture through its surface. The insulating sealing disk has aconvoluted surface wherein a portion of its surface underlies the ventaperture in the metal support disk when the cell is viewed in verticalposition with the end cap assembly on top. The portion of saidinsulating sealing disk underlying said aperture has a groove on theinside surface thereof preferably facing the cell interior. The groovehaving an open end and opposing closed base wherein the base of thegroove forms a thinned rupturable membrane. The rupturable membraneabuts the aperture in the metal support disk. When gas pressure withinthe cell rises said rupturable membrane penetrates through said apertureand ruptures thereby releasing gas directly into the surroundingenvironment through said aperture.

The insulating sealing disk comprises a plastic material having adownwardly extending wall slanted at an angle less than 90 degrees fromthe cell's central longitudinal axis and not parallel with saidlongitudinal axis. The downwardly extending wall of said insulating diskextends downwardly from a high point on the surface of the insulatingdisk and towards a lower point on its surface which is closer to thecell interior when the cell is viewed in vertical position with the endcap assembly on top. The metal support disk also has a downwardlyextending wall slanted at an angle less than 90 degrees from the cell'scentral longitudinal axis. The downwardly extending wall of the metalsupport disk extends downwardly from a high point on the surface thereofwhen the cell is viewed in vertical position with the end cap assemblyon top. There is at least one aperture in said downwardly extending wallof the metal support member against which the rupturable membrane abuts.Preferably the downwardly extending wall of the insulating sealing diskcan be slanted at an angle of between about 35 and 80 degrees from thecell's central longitudinal axis. The downwardly extending wall of theoverlying metal support disk is desirably slanted at the same angle,preferably an angle between about 35 and 80 degrees from the cell'scentral longitudinal axis, as the downwardly extending wall of theinsulating sealing disk. This allows the rupturable membrane portion ofthe downwardly extending wall of the insulating sealing disk to abut andlie flush against the aperture in the downwardly extending wall of themetal support disk. The downwardly extending wall of the insulatingsealing disk lies flush or nearly flush against the overlying downwardlyextending wall of said metal support disk.

The groove on the inside surface of the downwardly extending wall of theinsulating sealing disk forming the rupturable membrane portion ispreferably made so that it circumvents the center of the insulatingdisk. At least the portion of such circumventing rupturable membraneabutting said aperture in the metal support disk ruptures when the cellpressure rises to a predetermined level. The rupturable membrane may beof nylon or polypropylene. However, another preferred material for theinsulating sealing disk has been determined to be a polyetherurethanematerial, in particular a polytetramethyleneetherurethane material. Suchpolyetherurethane is a thermoplastic material with elastomericcharacteristics. It is alkaline resistant and highly durable. The endcap assembly of the invention allows the vent aperture to be made largerbecause of the inclined orientation of the downwardly sloping arm of themetal support disk. The undercut groove in the rupturable membraneallows for thinner membrane at the rupture point, that is, at the baseof the groove. This in turn allows for a reduction in design rupturepressures and accompanying small cell housing wall thickness, e.g.between about 4 and 12 mil (0.10 and 0.30 mm), thereby increasing theamount of cell internal volume available for active anode and cathodematerial. For example, the end cap assembly of the invention may allowfor a cell housing wall thickness of between 4 and 8 mils (0.10 and 0.20mm) for AA and AAA size cells and between about 10 and 12 mils (0.25 and0.30 mm) for C and D size cells.

The insulating seal disk for the alkaline cell may be molded byinjection molding plastic material such as nylon or polypropylene whichis durable and corrosion resistant in an alkaline environment. However,it has been determined to be advantageous to form insulating seal diskof a polyetherurethane material. The polyetherurethane materialavailable under the PELLETHANE 2103 series from Dow Chemical Co. hasbeen determined to be a preferred series of polyetherurethane materialfor alkaline cell sealing disk. The PELLETHANE 2103 series is apolyetherurethane comprising a tetramethyleneether repeat segment and isthus a polytetramethyleneetherurethane material. Such polyetherurethanecan be formed from the reaction product of a polytetramethyleneglycoland diisocyanate, thus forming a polytetramethyleneetherurethanematerial. The softness or hardness of the material may be controlled bythe number of repeat polytetramethyleneether units in the glycolreactant. A preferred polyetherurethane for the insulating seal disk isavailable under the trade designation PELLETHANE 2103-80AE from DowChemical Company. The PELLETHANE 2103-80AE polyetherurethane, which is apolytetramethyleneetherurethane material, has an ultimate tensilestrength of 5000 psi (34.5 mega Pascal) and an ultimate elongation of600 percent. The polyetherurethane class of material is chemicallyresistant to alkaline as is nylon. However, the polyetherurethane is athermoplastic material with elastomeric properties (an elastomericthermoplastic) whereas nylon is as thermoplastic essentially withoutelastomeric properties. Thus the polyetherurethane material is rubberyand more flexible than nylon.

The ultimate tensile strength, S, of the polyetherurethane material islower than that of nylon 66. This means that a membrane ofpolyetherurethane, designed to rupture at a given low pressure, forexample, between about 500 and 1000 psig for a AA size alkaline cell,would not require as thin a membrane thickness as nylon in order toachieve the target rupture pressure. This is an advantage since at lowlevel membrane thickness, e.g. of the level of about 0.10 mm or smallerit becomes more difficult to mold the membrane. The lower ultimatetensile strength, S, of the polyetherurethane material for theinsulating seal disk also means, that for a given target rupturepressure of the rupturable membrane, and given thickness of themembrane, the size of the abutting vent aperture in the metal supportdisk can be made smaller. This allows inclusion of secondary ventapertures within the structure of metal support disk, without muchcompromise in the structural integrity of the metal support disk. Thepresence of secondary vent apertures within the metal support diskaffords additional assurance that there will be proper venting of gasesfrom the cell interior in case the primary vent aperture in the metalsupport disk becomes plugged. Also, the polyetherurethane materialabsorbs less water than nylon 66 when exposed to hot humid conditions.This in turn means there is less chance of water entering the cellinterior from the external environment when the insulating sealing plug(insulating sealing disk 20) is formed of a polyetherurethane materialrather than nylon 66.

The peripheral edge of the insulating sealing disk abuts a portion ofthe inside surface of the housing. Another important advantage ofemploying a polyetherurethane material of construction for theinsulating seal disk is that after the housing (casing) edge has beencrimped over the insulating sealing disk, the peripheral edge of theinsulating seal disk stays tightly conformed to the housing surfacewhich it abuts. This is a result of the flexibility or elastomericproperties and softness of the polyetherurethane material. Such uniformsurface to surface conformity between the insulating sealing disk edgeand the housing edge stays in place over time. This eliminates the needto apply any separate seal coating (e.g. asphalt or polyamide sealcoating) between the peripheral edge of the seal disk and inside surfaceof the housing in order to assure a leak tight surface to surface sealbetween the insulating sealing disk and housing surface. This of coursedoes not preclude the addition of such seal coating to increase thelevel of seal protection between the peripheral edge of the insulatingseal and the housing. For example, some polyetherurethane may be madeharder than the preferred PELLETHANE 2103-80AE and application of suchseparate seal coating between the insulating sealing disk and housingcould be of more benefit in conjunction with the use of such harderpolyetherurethane material. The polyetherurethane material may be usedadvantageously in molding insulating sealing plugs or insulating sealingdisks for alkaline cells, regardless of the configuration of any thinnedportion or rupturable membrane portion therein.

The metal support disk preferably has a substantially flat centralportion with an aperture centrally located therein. Preferably, a pairof diametrically opposed same size apertures are located in thedownwardly extending wall of the metal support disk. After the cellactive components are inserted the end cap assembly is inserted into thecell's housing open end. The peripheral edge of the metal support diskand peripheral edge of the overlying end cap lie within peripheral edgeof the insulating sealing disk. The edge of the housing at its open endis then crimped over peripheral edge of the insulating seal disk. Theinsulating sealing disk edge in turn simultaneously crimps over both theperipheral edge of the metal support disk and peripheral edge of theoverlying end cap locking the end cap and metal support disk securely inplace over the insulating sealing disk. Thus, the insulating sealingdisk, metal support disk and overlying end cap become locked within theopen end of the housing thereby closing the cell housing. Surprisingly,the downwardly extending wall of the insulating disk is maintained in aflush or very nearly flush (contiguous) lie against the downwardlyextending wall of the overlying metal support disk even though enoughcrimping force must be applied during crimping to assure that theperipheral edge of the insulating sealing disk crimps over both themetal support disk edge and the end cap edge holding both edgespermanently locked therein. That is, the crimping forces do not disturbthe flush or nearly flush lie of the downwardly extending wall of theinsulating sealing disk against the overlying downwardly extending wallof the metal support disk.

The end cap assembly of the invention has an elongated anode currentcollector which has a head that passes through the central aperture inthe metal support disk so that it can be welded directly to theunderside surface of the end cap. The head of the anode currentcollector is preferably welded directly to the underside of the end capby electric resistance welding. There is no other welding of end capassembly components required. Laser welding need not be employedanywhere in the cell assembly, thereby making the cell assembly processmore efficient.

There are several common features in the end cap assembly of theinvention and the design shown in commonly assigned U.S. Pat. No.6,887,614 B2 (Duprey) with respect to the orientation of the rupturablemembrane abutting an aperture in the metal support disk and the use of apreferred undercut groove in the insulating seal to form the rupturablemembrane portion. However, the end cap assembly of the inventionrepresents an improvement over Duprey. In the end cap assembly of theinvention the use of an insulating washer between the end cap and cellhousing shoulder as shown in Duprey at FIG. 3 and as described thereinat col. 9, lines 36-51, has been eliminated. This has resulted in animproved end cap assembly design with fewer components. Instead in thepresent invention the peripheral edge of the insulating sealing disk iscrimped over both the edge of the end cap and the edge of the underlyingmetal support disk holding both metal support disk and end cap tightlylocked in place within the cell housing. This renders the end cap tamperproof, that is, the end cap cannot be readily removed by prying its edgefrom the cell as when the edge of the end cap is separated from thehousing by an insulating washer. The present end cap assembly of theinvention also eliminates the need to first weld the anode currentcollector to the underside of the metal support disk and then weld themetal support disk in turn to the end cap as in Duprey at FIG. 3. In theend cap assembly of the present invention the head of the anode currentcollector is welded directly to the end cap. There is no weldingrequired between the metal support disk and any other component, thussimplifying cell assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the drawingsin which:

FIG. 1 is a pictorial cut-away view of the end cap assembly of theinvention.

FIG. 1A is an elevational cross sectional view of the bottom portion ofthe cell.

FIG. 2 is an exploded view showing the components of the end capassembly of the invention.

FIG. 3 is a top perspective view of the insulating sealing disk.

FIG. 4 is a top perspective view of the metal support disk.

FIG. 5 is a top perspective view of the end cap.

DETAILED DESCRIPTION

A preferred structure of the end cap assembly 14 of the invention isillustrated in FIG. 1. The end cap assembly 14 of the invention hasparticular applicability to electrochemical cells comprising acylindrical housing 70 having an open end 15 and opposing closed end 17,wherein the end cap assembly 14 is inserted into said open end 15, toseal the cell. The end cap assembly 14 is particularly applicable tocylindrical alkaline cells of standard AAA (44×9 mm), AA (49×12 mm), C(49×25 mm) and D (58×32 mm) size. The end cap assembly 14 isparticularly useful for smaller size alkaline cells such as AAA and AAsize cell, but may be used advantageously in the C and D size cells aswell. Such alkaline cells, as cell 10 (FIGS. 1 and 1A), desirably has ananode 140 comprising zinc particles, a cathode 120 comprising MnO₂, withelectrolyte permeable separator 130 therebetween. The anode 140 andcathode 120 typically comprises an electrolyte of aqueous potassiumhydroxide. The anode 140 may comprise zinc particles, the cathode 120may comprise nickel oxyhydroxide, and the anode and cathode may comprisean electrolyte of aqueous potassium hydroxide.

The end cap assembly 14 of the invention comprises a metal support disk40, an underlying insulating sealing disk 20, and current collector 80penetrating through the central aperture 24 of sealing disk 20 and incontact with anode 140. A separate terminal end cap 60 of metal isstacked over the metal support disk 40 as shown in FIGS. 1 and 2. Aftercathode 120, separator 130 and anode 140 are inserted into housing 70,end cap assembly 14 is inserted into the housing open end 15. Theperipheral edge 72 of housing 70 is crimped over peripheral edge 28 ofinsulating sealing disk 20. The peripheral edge 28 of the insulatingsealing disk 20 is in turn crimped over both the peripheral edge 66 ofthe end cap 60 and the edge 49 of the metal support disk 40. In thecrimping process radial forces may be applied assuring that the edge 66of the end cap 60 bites into peripheral edge 28 of the insulatingsealing disk 20. The edge 49 of metal support disk 40 may also bite intoedge 28 of the insulating sealing disk 20.

The metal support disk 40 (FIGS. 1 and 4) preferably has a substantiallyflat central portion 43 with an aperture 41 centrally located therein.The metal support disk 40 is preferably formed of a disk of single piecemetallic construction having a convoluted surface. A portion of themetal support disk 40 has a downwardly sloping wall 45 and there is atleast one vent aperture 48 therethrough. Metal support 40 is constructedof a conductive metal having good mechanical strength and corrosionresistance such as nickel plated cold rolled steel, stainless steel, orlow carbon steel. The metal support disk 40 is preferably of carbonsteel having a convoluted surface of about 0.50 mm thickness.Preferably, a pair of diametrically opposed same size vent apertures 48are located in the downwardly extending wall 45 of the metal supportdisk 40 as shown best in FIG. 4. The downwardly extending wall 45 of themetal support disk 40 extends downwardly toward the cell interior from ahigh point 45 a on the wall 45 of said support disk 40 to a low point 45b on said wall 45 when the cell is viewed in vertical position with theend cap assembly 14 on top. The downwardly extending wall 45 of supportdisk 40 is preferably straight in the direction of downward slope or canhave a slightly convex surface contour (outward bulge) when viewed fromoutside the cell. Downwardly extending surface 45 terminates inperipheral edge 49.

The insulating sealing disk 20 (FIGS. 1 and 3) has a convoluted surfaceincluding downwardly extending wall 26 wherein a portion of its surfaceunderlies and abuts the aperture 48 in the metal support disk 40 whenthe cell is viewed in vertical position with the end cap assembly 14 ontop. The wall 26 of the sealing disk 20 extends downwardly from a highpoint 26 a on the surface thereof to a low point 26 b on the surfacethereof when the cell is viewed in vertical position with the end capassembly 14 on top. Surface 26 of insulating disk 20 is preferablystraight in the direction of downward slope (i.e. not bulging in or out)but may also have a slightly convex surface contour when viewed fromoutside the cell. Downwardly extending surface 26 terminates in upwardlyextending peripheral edge 28.

The portion of the downwardly extending surface 26 underlying saidaperture 48 in the metal support disk 40 (FIG. 1) has an undercut groove210 on the inside surface thereof facing the cell interior. The groove210 has an open end and opposing closed base. The groove base forms athinned rupturable membrane 23. The rupturable membrane 23 abuts theaperture 48 in the metal support disk 40. When gas pressure within thecell rises, said rupturable membrane 23 penetrates through said aperture48 and ruptures thereby releasing gas into the head space 18 above themembrane 23, that is, the space between the membrane 23 and overlyingend cap 60. The gas then passes to the external environment through ventapertures 65 in end cap 60 (FIGS. 1 and 5). Preferably, downwardlyextending wall 26 of insulating disk 20 lies flush against the insidesurface of downwardly extending wall 45 of metal support disk 40 duringassembly. Surprisingly, downwardly extending wall 26 of insulating disk20 is maintained in a flush or very nearly flush lie against thedownwardly extending wall 45 of metal support disk 40 even though enoughforce must be applied during crimping to assure that the peripheral edge28 of insulating sealing disk 20 is crimped tightly over both the metalsupport disk edge 49 and the end cap edge 66. That is, the crimpingforces do not dislodge the substantially flush lie of downwardlyextending wall 26 of insulating disk 20 against the downwardly extendingwall 45 of metal support disk 40. The crimping forces do not create onaverage more than about 0.50 mm space between the downwardly extendingwalls 26 and 45, and typically the crimping forces do not create onaverage more than about 0.35 mm space between the downwardly extendingwalls 26 and 45. The crimping forces may typically create on averagebetween about 0.1 mm and 0.50 mm space between the downwardly extendingwalls 26 and 45.

Groove 210 preferably runs circumferentially along the interior side 220of the downwardly extending wall 26 as shown best in FIGS. 1 and 3. Thegroove 210 forms a thinned portion 23 running preferablycircumferentially along the interior side (underside) of downwardlyextending wall 26 of insulating sealing disk 20 (FIG. 1). Circumventinggroove 210 (FIG. 1) forms a thinned portion, namely, circumventingmembrane 23 at the base of groove 210. The thinned portion 23 forms arupturable membrane which faces and preferably abuts downwardlyextending wall 45 of the metal support disk 40 as shown in FIG. 1. Therecan be one or more apertures 48 in downwardly extending wall 45 of metalsupport disk 40 (FIGS. 1 and 4). Preferably there are two apertures inthe surface of downwardly extending wall 45 as shown in FIG. 4. If twoapertures 48 are employed they are desirably of about the same size andare located diametrically opposite each on downwardly extending wall 45(FIG. 4). The portion of the circumventing thinned membrane 23 runningdirectly under vent aperture 48 forms a rupturable portion. When gaswithin the cell builds up to a predetermined level, the portion ofmembrane 23 immediately under aperture 48 will stretch into the apertureuntil it ruptures under tension thereby releasing gas from within thecell. The cell's internal pressure is immediately reduced as the gasescapes to the environment through overlying end cap vent apertures 65.

The opposing groove walls 212 a and 212 b defining the depth of undercutgroove 210 do not have to be of any particular shape of curvature.However, from the standpoint of ease of manufacture the groove walls 212a and 212 b can be vertically oriented or may be slanted so that themouth of groove 210 is wider than the base (rupturable membrane portion23) of the groove. The angle of 212 a does not play a factor in therupturability of membrane 23, since the membrane is preferably intendedto rupture in tension, not in shear. Walls 212 a and 212 b can beconveniently at right angle to rupturable membrane 23 at the base ofgroove 210 or can form an obtuse angle with the rupturable membrane 23as shown in FIG. 1. Alternatively, groove walls 212 a and 212 b can beformed of flat or curved surface. Desirably, walls 212 a and 212 b eachform flat surfaces forming an obtuse angle, desirably between about 120and 135 degrees, with rupturable membrane 23 so the open end of thegroove 210 is slightly wider than the groove base forming membrane 23.Such preferred embodiment gives circumventing groove 210 a trapezoidalshape as shown in FIG. 1. Such configuration is desirably from thestandpoint of ease of manufacture by injection molding and does noteffect the rupturability of membrane 23.

The downwardly extending wall 26 and rupturable membrane portion 23therein is desirably slanted at an acute angle (angle less than 90°)from the cell's central longitudinal axis 190 as illustrated in FIG. 1.In such configuration downwardly extending wall 26 and membrane portion23 therein is not parallel to the cell's central longitudinal axis.Preferably downwardly extending wall 26 is slanted at an acute anglebetween about 35 and 80 degrees from longitudinal central axis 190 (FIG.1). Likewise, downwardly extending wall 45 of support disk 40 ispreferably slanted at the same acute angle as the downwardly extendingwall 26 of seal disk 20, namely between about 35 and 80 degrees fromcentral axis 190. Thus, when the support disk 40 is placed over sealdisk 20, the downwardly extending wall 45 of support disk 40 will abutand lie flush against the downwardly extending wall 26 of seal disk 20and rupturable membrane 23 will abut aperture 48. As above indicated ithas been determined that a flush (or very nearly flush) lie of the metalsupport disk downwardly extending wall 45 against the seal diskdownwardly extending wall 26 can be maintained, despite the greatercrimping forces needed to crimp the seal edge 28 over both end cap edge66 and metal support edge 49 simultaneously. The slanted orientation ofdownwardly extending wall 45 of the metal support disk 40 allows largerdiameter apertures 48 to be made in the downwardly extending wall 45 fora given overall height of support disk 40. This in turn allows themembrane 23 of a given small thickness to rupture at lower thresholdpressure thereby allowing the cell housing 70 wall thickness to bereduced. Reduction in housing 70 wall thickness increases the cellinternal volume available for anode and cathode active material therebyincreasing cell capacity.

In the absence of a groove forming a rupturable membrane in the seal,that is, if the entire portion of downwardly sloping wall 26 abuttingaperture 48 is of uniform constant thickness and forms the rupturablemembrane, the following relationship has been determined to applyapproximately between the desired rupture pressure P_(R), the radius “R”of the vent aperture 48, and thickness “t” of the resulting constantthickness membrane, where “S” is the ultimate tensile strength of therupturable material. Even if there is a groove forming rupturablemembrane the following formula plays a role in determining rupturepressure.

P _(r) =t/R×S  (I)

Insulating seal disk 20 may be formed of a single piece construction ofplastic insulating material. In the embodiment of the end cap assembly14 shown in FIG. 1 the rupturable membrane 23 within seal disk 20 abutsaperture 48 in metal support disk 40. Insulating seal disk 20 may bemolded by injection molding nylon which is durable and corrosionresistant. However, it has been determined to be advantageous to forminsulating seal disk 20 of a polyetherurethane material. Preferredpolyetherurethane material may be selected from the PELLETHANE 2103series polyetherurethane from Dow Chemical Co. The PELLETHANE 2103series polyetherurethane are thermoplastic materials which exhibitelastomeric properties. The PELLETHANE 2103 series polyetherurethanegenerally have ultimate tensile strength (ASTM D412 test) less than theultimate tensile strength of nylon 66 and an ultimate elongation percent(ASTM D412 test) greater than 200 percent, typically greater than 300percent, which is much greater than nylon 66. (Nylon 66 has an ultimateelongation of about 90 percent.) Such PELLETHANE material isthermoplastic (softens when exposed to heat but returns to its originalcondition when cooled) and yet exhibits elastomeric properties as well.That is, PELLETHANE material, is an “elastomeric thermoplastic”. Bycontrast nylon is a thermoplastic but does not exhibit elastomericproperties. Thus the term “elastomeric thermoplastic” as used hereinshall mean a thermoplastic polymeric material which also has an ultimateelongation greater than about 200 percent, thereby also impartingelastomeric properties to the thermoplastic material.

A preferred polyetherurethane for insulating seal disk 20 is availableunder the trade designation PELLETHANE 2103-80AE from Dow ChemicalCompany. (The 80AE represents 80 shore on the ASTM A shore hardnessscale. The E is a medical grade certification designation.) ThePELLETHANE 2103-80AE polyetherurethane has an ultimate tensile strengthof 5000 psi (34.5 mega Pascal) and an ultimate elongation of 600percent. Another polyetherurethane which can be used advantageously forinsulating seal disk 20 is available under the trade designationPELLETHANE 2103-65D. (The 65D means 65 shore on the ASTM D shorehardness scale.) The PELLETHANE 2103-65D has an ultimate tensilestrength of 5750 psi (39.6 mega Pascal) and an ultimate elongation of360 percent. However, the PELLETHANE 2103-80AE material is somewhatsofter than PELLETHANE 2103-65D material and therefore more preferred asa material of construction for seal disk 20. The polyetherurethanematerial is chemically resistant to alkaline as is nylon. However, thepolyetherurethane is a thermoplastic material with elastomericproperties whereas nylon is as thermoplastic essentially withoutelastomeric properties. The polyetherurethane material is rubbery andmore flexible than nylon. For example PELLETHANE 2103-80AE has anultimate elongation of 600 percent whereas nylon 66 has an ultimateelongation of 90 percent. Thus, by comparison nylon is a rigidthermoplastic.

As above indicated the ultimate tensile strength, S, of thepolyetherurethane material is lower than that of nylon. For example,PELLETHANE 2103-80AE polyetherurethane has an ultimate tensile strengthof 5000 psi (34.5 mega Pascal) whereas nylon 66 has an ultimate tensilestrength of between about 7000 and 11000 psi (48.26 and 75.83 megaPascal). This means that a polyetherurethane rupturable membranedesigned to rupture at a given low pressure, for example, between about500 and 1000 psig for an AA size alkaline cell, would not require asthin a membrane thickness as nylon in order to achieve such rupturepressure. This results in an advantage in molding the polyetherurethanerupturable membrane compared to nylon, since it becomes more difficultto mold a rupturable membrane of very small thickness, e.g. of the levelof 0.1 mm or smaller.

The lower ultimate tensile strength, S, of the polyetherurethanematerial for insulating seal disk 20 also means (see above Equation I)that for a given target rupture pressure P_(r) of membrane 23, and giventhickness, t, of membrane 23, the abutting vent aperture 48 radius, R,in metal support disk 40 can be made smaller. This allows inclusion ofsecondary vent apertures 48 within the structure of metal support disk40, e.g., within downwardly extending wall 45 of metal support disk 40.The presence of secondary vent apertures affords additional assurancethat there will be proper venting of gases within the cell interior.That is, in case the primary vent aperture 48 becomes clogged, membrane23 will nevertheless rupture against another (secondary) vent aperture48 located within sloping wall 45 of metal support disk 40. Sincesmaller vent apertures 48 in the metal support disk 40 can be employedwhen the insulating sealing disk is composed of polyetherurethanematerial, this results in a stronger metal support disk 40 as comparedto the same metal support disk having same number but larger size ventapertures.

Also the polyetherurethane material absorbs less water than nylon 66when exposed to hot humid conditions. This in turn means there is lesschance of water entering the cell interior from the external environmentwhen seal disk 20 is formed of a polyetherurethane material rather thannylon 66. When nylon or other alkaline resistant thermoplastic such aspolypropylene is used for insulating sealing disk 20 a sealing coat suchas an asphalt or polyamide coating is often applied between theperipheral edge 28 a of the sealing disk and inside surface of housing70 or between the anode current collector 80 and hub 22 of theinsulating seal disk 20.

Another important advantage of employing a polyetherurethane such asPELLETHANE 2103-80AE for insulating seal disk 20 is that it eliminatesthe need to apply any separate seal coating between the peripheral edge28 a of the seal disk 20 and inside surface of casing 70. It alsoeliminates the need to apply a coating of sealing material between anodecurrent collector 80 and hub 22 of insulating seal disk 20.

The polyetherurethane material available under the PELLETHANE 2103series from Dow Chemical Co. has been determined to be a preferredseries of polyetherurethane material for alkaline cell sealing disk 20.As above indicated the PELLETHANE 2103-80AE has been determined to bethe more preferred material within this series for the alkaline cellinsulating sealing disk 20. The PELLETHANE 2103 series is apolyetherurethane comprising a tetramethyleneether repeat segment and isthus a polytetramethyleneetherurethane.

Such polytetramethyleneetherurethane can be formed as the reactionproduct of a tetramethyleneglycol and diisocyanate as follows:

HO—[CH₂CH₂CH₂CH₂—O]_(m)—H+OC═N—R—N═CO-→tetramethyleneglycol diisocyanate

HO—([CH₂CH₂CH₂CH₂—O]_(m)—CO—NH—R—NH—CO)_(n)-polytetramethyleneetherurethane  (II)

The degree of softness or hardness of thepolytetramethyleneetherurethane may be controlled by varying the numberof tetramethylene repeat units “m” in the polyether segment. Thediisocyanate may have the group “R” selected from aromatic, aliphatic orcycloaliphatic as given for example in U.S. Pat. No. 4,394,491. Themolecular weight of the polymer is sufficiently high so that it hasuseful physical properties. The molecular weight of thepolyetherurethane (II) is a function of the number of polytetramethylenesegments, m, and the overall number of repeat units, n. A commonaromatic diisocyanate which may be employed in the above reaction II istoluene diisocyanate. Another aromatic diisocyanate which may beemployed is naphthylene—1,5 diisocyanate. A common aliphaticdiisocyanate which may be employed in the above reaction ishexamethylene diisocyanate. A common cycloaliphatic diisocyanate whichmay be employed in the above reaction is cyclohexane-1,4 diisocyanate.

The polyether repeat segment in the polyurethane product preferablycomprises a tetramethyleneether, that is, formed from employing atetramethylene glycol as a reactant with the diisocyanate as shown inthe above reaction II. Other glycols may be used as reactants, thusleading to other types of ether repeat units, that is, other than thetetramethyleneether unit in the polyurethane product. For example, theglycol used in the above reaction may be selected from ethylene glycol;1,3-propylene glycol; 1,2-propylene glycol; 1,4-butylene glycol;1,3-butylene glycol; 1,2-butylene glycol; 1,5-pentane diol; hexane diol;1,7-heptane diol; glycerol, and 1,1,1-trimethylolpropane. The polyetherrepeat segment in the polyurethane product may also be formed form apolyalkylene polyether polyol. Such polyols may be prepared from otherstarting material such as tetrahydrofuran and alkylene oxidetetrahydrofuran copolymers; epihalohydrins such as epichlorohydrin, aswell as arylalkylene oxides such as styrene oxide. Other polyols whichmay be used as reactant with the diisocyanate to form apolyetherurethane product is given in U.S. Pat. No. 4,394,491.

Cell Vent Rupture Test and Leakage Tests with Alkaline Cell Employing aPolyetherurethane Sealing Disk

The effectiveness of the employing an insulating sealing disk 20 moldedof polyetherurethane material is demonstrated in the following tests.Identical AA size zinc/MnO₂ alkaline cells were built as shown in FIG. 1with end cap assembly 14 configuration as shown in FIG. 2. As such theperipheral edge 28 a of insulating sealing disk 20 abutted a portion ofthe inside surface of housing 70. The sealing disk 20 as shown best inFIGS. 2 and 3 was molded of polyetherurethane material available underthe trade designation PELLETHANE 2103-80AE, which is apolytetramethyleneetherurethane from Dow Chemical Co. There was acircumferential groove 210 forming rupturable membrane 23 within theseal disk downwardly extending wall 26 as shown in FIG. 1. The width ofgroove 210 was about 0.5 mm. The rupturable membrane 23 at the base ofgroove 210 had a thickness of about 0.15 mm. There were twodiametrically opposed vent apertures 48 in metal support disk 40 asshown in FIG. 1. For the leakage tests both vent apertures 48 had adiameter of about 1.8 mm.

For the membrane rupture tests the same rupturable membrane 23 thicknessof about 0.15 mm was used with a circumferential groove 210 width ofabout 0.5 mm. There were also two same sized diametrically opposed ventapertures 48. But in some cells the vent aperture diameter were atdiameter of 1.0 mm, other cells had both vent apertures 48 at 0.9 mmdiameter, and others had both apertures at 0.8 mm diameter.

There were no seal coatings of any type applied to the area between theinsulating sealing disk peripheral edge 28 a and abutting peripheraledge 72 of casing 70. There was also no seal coatings of any typeapplied to the area between anode current collector 80 and hub 22 of theinsulating sealing disk 20. Cells were tested for proper rupture ofmembrane 23 as gas pressure within the cell was increased.

In a separate test fresh AA cells were subjected to leakage tests. TheAA cells were subjected first to a 12 cycle temperature stress test(TST). The cells were then inspected for leakage. After completion ofthe 12 cycle temperature stress test the same cells were then subjectedto a 12 week ambient test and then inspected again for leakage.

Rupture Vent Pressure

Groups of AA zinc/MnO₂ alkaline cells were tested for successful ruptureof the above referenced rupture membrane 23 formed of PELLETHANE2103-80AE material. The rupturable membrane 23 had a thickness of about0.15 mm. The circumferential groove width 210 was about 0.5 mm. Therewere two same size diametrically opposed vent apertures 48 in metalsupport disk 40. In one group of cells the vent aperture 48 diameter was1.0 mm; in a second group of cells both vent apertures 48 had a diameterof 0.9 mm, and in a third group of cells both vent apertures 48 haddiameter at 0.8 mm. The cells was subjected to abusive conditionsthereby causing gas pressure within the cell to increase. The gaspressure within the cell was allowed to increase until the PELLETHANEmembrane 23 ruptured thereby releasing gas through vent aperture 48. Thegas then passed to the environment through apertures 65 in end cap 60.The membrane 23 ruptured successfully when gas pressure within the cellreached an average level of about 1170 psi with the 1.0 diameter ventapertures, an average level of about 1145 psi with the 0.9 mm ventapertures, and an average level of about 1320 psi with the 0.8 ventapertures. The cells were disassembled. It was confirmed from inspectionthat the portion of membrane 23 which abutted the vent apertures 48ruptured cleanly without plugging the vent aperture, thus allowing gasfrom within the cell interior to escape therethrough.

12 Cycle Temperature Stress Test (TST)

Fresh AA cells (FIG. 1) with the sealing disk 20 molded of PELLETHANE2103-80AE material were subjected to a 12 cycle temperature stress test.There were no separate seal coating applied between the peripheral edge28 a and the inside surface of housing 70. There was also no sealcoating applied between the hub 22 of the insulating sealing disk 20 andanode current collector 80. The protocol for each cycle of this testinvolved subjecting assembled AA cells to heating for 1 hour in an ovenmaintained at 71° C. by forced circulating hot air. The cells were thenremoved from the oven and placed directly in a freezer. The cells wereleft in the freezer at −29° C. for 1 hour. The cells were removed fromthe freezer and placed on a table and remained on the table for 1 hourat ambient temperature (21° C.). This completed one cycle. The cellswere then placed back in the oven at 71° C. for 1 hour to begin a newcycle. The cells were subjected in this manner to 12 cycles. At theconclusion of the 12 cycle test protocol, the cells were inspected forleakage.

Of the 7 AA cells tested there was no leakage observable in any of thecells.

12 Week Ambient Test

Following the above 12 cycle temperature stress test (TST) the samecells were then subjected to an additional test, namely a 12 weekambient test. After the cells were subjected to the 12 cycle temperaturestress test the same cells were then left out in open ambient air atabout 21° C. for one week duration. The cells were then inspected forleakage.

Of the 7 AA cells tested there was no leakage observable in any of thecells. These results show the effectiveness of the polyetherurethanematerial as a material of construction for the sealing disk. Inparticular these results are impressive, since as above indicated therewere no seal coatings of any kind applied to the area between thesealing disk 20 and casing 70 or between the anode current collector 80and hub 22 of the sealing disk. The very effective sealing properties ofthe polyetherurethane material (PELLETHANE 2103-80AE) is attributed to anumber of properties of this material which are present in combination.Firstly the material is resistant to attack by alkaline electrolyte. Thematerial unlike nylon or polypropylene has elastomeric properties. Theelastomeric properties of the polyetherurethane insulating sealing disk20 allow for a lasting conformal surface to surface fit between theperipheral edge 28 a of the insulating seal disk 20 and the edge 72 ofhousing 70 upon crimping housing casing edge 72 over the edges of theinsulating sealing disk 20 and end cap 60. That is, since thepolyetherurethane (PELLETHANE 2103-80AE) material has elastomericproperties and has a relatively soft texture the surface to surfacecontact and fit between insulating sealing disk edge 28 a and casingedge 72 does not loosen or weaken once the casing edge 72 is crimpedover sealing disk edge 28 a. Thus, alkaline electrolyte is not able topenetrate the area between the insulating sealing disk and casing, eventhough the cell was subjected to the above two back to back leakagetests.

In this respect the elastomeric properties of the polyetherurethanesealing disk appears to have an advantage over alkaline cell sealingdisks formed of conventional nylon or polypropylene which is more rigidand thus more apt to separate in time from close, uniform contact withcasing edge 72. As a result of the elastomeric properties of aninsulating sealing disk 20 formed of polyetherurethane (PELLETHANE2103-80AE) as demonstrated in the above tests, a tight conformal surfaceto surface fit between the insulating sealing disk edge 28 a and thecasing edge 72 is maintained even though there is no separate sealcoating applied between these two surfaces. This of course does notpreclude the use of such separate seal coating for added protectionagainst leakage. For example, a seal coating of asphalt or polyamidecoating or other sealing coating may nevertheless be applied between thesealing disk edge 28 a and casing edge 72 for additional protectionagainst leakage. Such seal coating may be beneficial when employingother grades of polyetherurethane material such as PELLETHANE 2103-65D,which is not quite as soft and elastomeric as PELLETHANE 2103-80AE.

The polyetherurethane material as described herein has been applied, byway of example, to a specific embodiment of the insulating seal disk 20as shown in FIGS. 1, 2 and 3. This insulating seal disk 20 has acircumferential groove 210 with thinned region of remaining material atthe base of the groove forming rupturable membrane 23. There aredisclosed in the art other configurations of alkaline cell insulatingsealing disks which contain thinned portion forming the rupturablemembrane in the form of slits or grooves within the insulating disk asshown, for example, in U.S. Pat. No. 4,237,203 and U.S. Pat. No.6,991,872. Such thinned portions or rupturable membranes within theinsulating disk are designed to rupture when gas pressure within thecell builds to a predetermined level. A pointed or other protrudingmember can be oriented above the rupturable membrane to assist inrupture of the membrane as shown in U.S. Pat. No. 3,314,824. Therupturable membrane can be in the form of one or more “islands” of thinmaterial within the insulating disk as shown in U.S. Pat. No. 4,537,841;U.S. U.S. Pat. No. 5,589,293; and U.S. Pat. No. 6,042,967.

The polyetherurethane material as described herein may be used to moldor form alkaline cell insulating disks regardless of whether therupturable membrane portion therein is of a grooved or slitconfiguration or of the “island” type configuration. Thus, it is notintended that polyetherurethane material be limited to application toany particular alkaline cell insulating sealing disk configuration or toany particular shape or configuration for any thinned portion forming arupturable membrane therein. For example, the housing surface 70 andsealing disk may be of oblong or elliptical configuration instead ofcylindrical, or it may be of prismatic or cuboid shape. The grooves 210and underlying thinned portions forming the rupturable membrane 23 inthe insulating sealing disk 20 may be of the island type or they may becircumferential or segmented. If segmented (discontinuous) grooves andunderlying thinned portion 23 in the sealing disk 20 are employed theymay be straight, arcuate or curvilinear in shape. The polyetherurethanematerial herein described can be advantageously used to mold or forminsulating sealing disks for alkaline cells, regardless of the shape orconfiguration of the disk or any thinned portion therein forming arupturable membrane. The polyetherurethane material could possibly alsobe useful in forming insulating sealing disks for other cell types, forexample, cells having a lithium or lithium alloy anode. Such cellsemploy nonaqueous electrolytes comprising a lithium salt dissolved in anorganic electrolyte. The extent of the usefulness of thepolyetherurethane material for sealing disks of such nonaqueous cellswould be determined by experimentation, to assure compatibility betweenthe polyetherurethane material and the electrolyte.

As illustrated best in FIGS. 1 and 3, insulating disk 20 has a centralboss or hub 22 with aperture 24 through the center thereof. Boss 22forms the thickest and heaviest portion of disk 20. The peripheral edgeof boss 22 terminates in downwardly extending wall 26 which extendsdownwardly from a high point 26 a on said wall 26 to a low point 26 bthereon when the cell is viewed in vertical position with the end capassembly on top (FIGS. 1 and 3). Similarly, the peripheral edge of thecenter portion 43 of support disk 40 terminates in downwardly extendingwall 45 from a high point 45 a on said wall 45 to a low point 45 bthereon (FIGS. 1 and 4).

The above described insulating seal disk 20 configuration also placesthe rupturable membrane 23 closer to the end cap 60. This means thatthere is more internal space available within the cell for activematerials. Location of the rupturable membrane 23 on downwardlyextending wall 26 of the insulating disk 20 permits gas and otherinternal components to pass unobstructed from the cell interior throughaperture 48 in the metal support disk, then directly out to theenvironment through apertures 65 in the end cap 60 after membrane 23ruptures. Such passage of gas from the cell interior to the environmentis unobstructed even when the cell is connected to another cell or adevice being powered.

It has been possible to reduce cell gassing through use of multiplegassing inhibitors. It is desirable to have the aperture 48 radius largeand the thickness of the constant thickness membrane as small aspossible. This allows rupture of the membrane if desired at lowerthreshold pressures, P, of gas buildup in the cells. Thus for a givencell size, there is a practical lower limit to the burst pressuredetermined by a maximum aperture radius and minimum membrane thicknessachievable. The addition of an undercut groove 210 forming a rupturablemembrane provides additional variables, such as groove depth and width,with which to manipulate the burst pressure to lower levels.

In the end cap assembly 14 the ratio of the rupturable membrane width(that is, the width of the base of groove 210) to the thickness of therupturable membrane 23 is typically between about 2.5 to 1 and 12.5to 1. The design of the end cap assembly 14 can accommodate an aperture48 typically as large as between about 1.8 and 10 mm (circular diameter)in downwardly slanted wall 45 of metal support disk 40, for common cellsizes between AAA and D size cells.

The following lower level rupture pressures for membrane 23 aredesirable in connection with the end cap assembly 14 of the invention.For AAA alkaline cells the target rupture pressure of membrane 23 isdesirably between about 900 to 1800 psig (6.21 mega Pascal and 12.41mega Pascal gage). For AA alkaline cells the target rupture pressure ofmembrane 23 is desirably between about 500 to 1500 psig (3.45 megaPascal and 10.34 mega Pascal gage). For C size alkaline cells the targetrupture pressure for membrane 23 is desirably between about 300 and 550psig (2.07 mega Pascal and 3.79 mega Pascal gage). For D size alkalinecells the target rupture pressure for membrane 23 is desirably betweenabout 200 and 400 psig (1.38 mega Pascal and 2.76 mega Pascal gage).Such rupture pressure ranges are intended as non limiting examples. Itwill be appreciated that the end cap assembly 14 is not intended to belimited to these rupture pressure ranges as the present end cap assembly14 can be employed as well with higher and even lower rupture pressures.

With the above indicated rupture pressures ranges for the given cellsize, housing 70 of nickel plated steel may typically have a small wallthickness, desirably between about 0.006 and 0.012 inches (0.15 and 0.30mm), preferably between about 0.006 and 0.008 inches (0.15 and 0.20 mm)for the AA and AAA, and between about 0.010 and 0.012 inches (0.25 and0.30 mm) for the C and D. The smaller wall thickness for housing 70 isdesired, since it results in increased internal volume of the cellpermitting use of more anode and cathode material, thereby increasingthe cell's capacity. The end cap assembly 14 permits the above describedrupture pressures to be achieved for the given cell size, and has anadditional feature that the end cap 60 is “tamper proof”. That is, sincethe edge 66 of end cap 60 is crimped under the peripheral edge 28 ofinsulating sealing disk 20, it cannot be readily pried away from the endcap assembly. Thus, in the present end cap assembly 14 design, the cellcontents as well are very secure and well protected against malicioustampering. Additionally, in the end cap assembly 14 of the invention thehead 87 of anode current collector nail 80 is welded directly to theunderside of end cap 60. This can be achieved by simple electricresistance welding. In the present end cap assembly 14 there is no needfor welding of any other cell components, and there is no need for laserwelding, thus simplifying cell construction.

In order to allow for the use of larger size apertures 48 in the contextof end cap assembly herein described, it has been determined that thiscan be achieved best by orienting the insulating seal wall 26 containingrupturable membrane 23 at a slant, that is, not parallel to thelongitudinal axis 190. Preferably, seal wall 26 and abutting metalsupport surface 45 are slanted downwardly at an angle, preferablybetween about 35 and 80 degrees from the central longitudinal axis 190.This provides more available surface area from which to form aperture48.

In keeping with the desire to reduce the burst pressure of the cell, ithas been determined that this can be achieved by forming an undercutgroove 210 on the inside surface of downwardly sloping wall 26 ofsealing disk 20. Such undercut groove 210 can be formed, for example,circumventing the center of sealing disk 20, during injection molding atthe time of forming the sealing disk 20.

In a preferred embodiment employing an AA size alkaline cell, by way ofnonlimiting example, the rupturable membrane 23 can be designed torupture when gas within the cell builds up to a level of between about500 to 1500 psig (3.45 mega Pascal and 10.34 mega Pascal gage). Therupturable membrane portion 23 underlying apertures 48 in metal supportdisk 40 is advantageously formed of a polyetherurethane material, e.g.PELLETHANE 2103-80AE from Dow Chemical Co. as above indicated.Alternatively, rupturable membrane 23 may be formed of nylon, preferablynylon 66 or nylon 612, but can also be of other material such aspolypropylene. (Nylon 66 is more cost effective than nylon 612 and ispreferred in this regard.) Groove 210 can have a width between about0.08 and 1 mm, desirably between about 0.08 and 0.8 mm. Groove 210preferably runs circumferentially around the inside surface 220 ofdownwardly extending wall 26 of insulating disk 20. A segment ofcircumferential groove 210 runs immediately under apertures 48 in metalsupport disk 40. Alternatively, the groove 210 need not be circumventingbut can be formed so that individual grooves are cut immediately underapertures 48 with the portions of the inside surface of wall 26therebetween left smooth and uncut. The apertures 48 can be of circularshape having a diameter of between about 1.8 and 10 mm, corresponding toan area of between about 2.5 and 78.5 mm², typically between 2 and 9 mm(circular diameter), corresponding to an area between about 3.1 and 63.6mm², for common cell sizes between AAA and D size cells. It should berecognized that apertures 48 can be of other shape such as oblong orelliptical. Apertures 48 can also be of rectangular or polygonal shapeor irregular shapes comprising a combination of straight and curvedsurfaces. The effective diameter of such oblong or polygonal shape orother irregular shape is also desirably between about −2 and 9 mm. Theeffective diameter with such shapes can be defined as the minimumdistance across any such aperture.

When the target rupturable pressure is between about 500 to 1500 psig(3.45 and 10.34 mega Pascal gage) for an AA cell or between about 900 to1800 psig (6.21 and 12.41 mega Pascal gage) for an AAA size cell, theratio of the groove width (width of membrane 23 at base of groove) tothe thickness of rupturable membrane 23 is desirably between about 2.5:1and 12.5:1. In keeping with this range of ratio, the groove width at thebase of the groove is desirably between about 0.1 and 1 mm, preferablybetween about 0.4 and 0.7 mm and the thickness of rupturable membrane 23is between about 0.08 and 0.25 mm, desirably between about 0.10 and 0.20mm. The apertures 48 have can have a diameter typically between about1.8 and 4.5 mm, corresponding to an area between about 2.5 and 16 mm².

When C and D alkaline cells are employed rupturable membrane 23 isdesirably designed to rupture at lower pressures. For example, for Csize cells the target rupture pressure may be between about 300 and 550psig (2.07 and 3.79 mega Pascal gage). For D size cells the targetrupture pressure may be between about 200 and 400 psig (1.38 and 2.76mega Pascal gage). The same ratio of the groove width (width of membrane23 at base of groove) to the thickness of rupturable membrane 23 isdesirably between about 2.5:1 and 12.5:1 is also applicable.

In general irrespective of cell size, it is desirable to maintain aratio of the thickness of the rupturable membrane 23 to the thickness ofdownwardly extending seal wall 26 immediately adjacent membrane 23 to be1:2 or less, desirably between about 1:2 and 1:10, more typicallybetween about 1:2 and 1:5. In such embodiment the rupturable membrane 23thickness is desirably between about 0.08 and 0.25 mm, preferablybetween about 0.1 and 0.2 mm. The apertures 48 through which themembrane 23 ruptures desirably have a diameter between about 1.8 and 10mm.

In assembly after the anode 140, cathode 120 and separator 130 areinserted into the cell housing 70, the end cap assembly 14 is insertedinto the housing open end 14. The metal support disk 40 may first bepressed onto the insulating sealing disk 20 so that the top surface 43of the boss 22 of sealing disk 20 penetrates into central aperture 41 ofmetal support disk 40. The downwardly extending wall 26 of theinsulating disk 20 lies flush against the inside surface of downwardlyextending wall 45 of the overlying metal support disk 40. The insulatingsealing disk 20 with metal support disk 40 contained therein may then beinserted into the open end 15 of housing 70. The lower portion of theinsulating seal peripheral edge 28 rests on circumferential bead 73 inthe cell housing side wall 74. The head 87 of current collector nail 80is welded, preferably by electric resistance welding, to the undersideof end cap 60.

The current collector 80 is then inserted through aperture 41 in themetal support disk 40 and then through underlying central aperture 24 inthe insulating sealing disk 20 until the tip 84 of the current collectorpenetrates into the anode 140 material. The underside of the attachedend cap 60 comes to rest against the top flat surface 43 surroundingaperture 41 of metal support disk 40. Both edges 49 of the metal supportdisk 40 and edge 66 of the overlying end cap 60 lie within peripheraledge 28 of insulating sealing disk 20 as shown in FIG. 1. The edge 72 ofthe housing 70 is then crimped over peripheral edge 28 of the insulatingseal disk 20. The insulating sealing disk edge 28 in turn crimps overboth edge 49 of the metal support disk 40 and edge 66 of end cap 60locking the end cap 60 and underlying metal support disk 40 securely inplace over the insulating sealing disk 20. Thus, the insulating sealingdisk 20, metal support disk 40 and overlying end cap 60 become lockedwithin the open end 15 of the housing thereby closing the cell housing.Radial compressive forces may be applied to housing 70 during crimpingto assure that the peripheral edge 66 of end cap 60 bites into theperipheral edge 28 of the insulating sealing disk 20 and that the metalsupport disk edge 49 becomes radially compressed thereby helping toachieve a tight seal. The edge of 66 of the end cap 60 is not accessibleand thus the end cap 60 is considered to be tamper proof, that is,cannot be readily pried away from the cell assembly.

In another embodiment of the sealing disk 20, the disk configuration canbe the same as shown in FIG. 1 and FIG. 3 except that groove 210 can beformed by cutting or stamping a die or knife edge, with or without theaid of a heated tool, into the underside 220 of downwardly extendingwall 26 of sealing disk 20 after the disk is formed. In such embodimentthe sealing disk 20 can be first formed by molding to obtain adownwardly extending wall 26 of uniform thickness, that is, withoutgroove 210. A die having a circumferential cutting edge can then beapplied to the underside surface 220 of the sealing disk downwardlyextending wall 26. A circumferential or arcuate cut forming groove 210of width less than 1 mm, desirably between about 0.08 and 1 mm,preferably between 0.08 and 0.8 mm can be made in this manner to theunderside surface 220 of downwardly extending wall 26 of sealing disk20. Groove 210 forms the rupturable membrane 23 at the base of groove.The rupturable membrane 23 formed by groove 210 forms a weak area in thesurface of downwardly extending wall 220 of the sealing disk. Groove 210can be made by the use of a cutting die, e.g., a die having a raisededge (knife edge) which is pressed onto the underside of downwardlyextending wall 26. The groove 210 made in this manner allows themembrane 23 at the base of groove 210 to be formed thinner than if thegroove 210 is molded into downwardly extending wall 26. Groove 210formed by a cutting die can thus result in a rupturable membrane 23 ofvery small width and very small thickness. The membrane 23 formed bygroove cut 210 (FIG. 1) can be designed to rupture at the desired targetpressure by adjusting the depth the cut, which in turn forms arupturable membrane 23 of a desired thickness at the base of the cut.

The membrane 23 formed by groove cut 210 abuts the underside ofdownwardly extending wall 45 of metal support disk 40. A portion ofmembrane 23 can underlie one or more apertures 48 in downwardlyextending wall 45 of metal support disk 40 in the same manner asdescribed with respect to the embodiment shown in FIG. 1. It will beappreciated that groove cut 210 (FIGS. 1 and 3) does not have to be inthe shape of continuous closed circle, but can be an arcuate segment,preferably long enough so that the portion of groove 210 underlyingaperture 48 is continuous over the width of aperture 48. That is, groove210 does not have to extend to portions 220 (FIG. 1) of the downwardlyextending wall 26 not overlaid by aperture 48.

In a specific embodiment, by way of a non limiting example, irrespectiveof cell size, the sealing disk 20 can be of polyetherurethane, e.g.PELLETHANE 2103-80AE, or nylon 66, and the groove cut 210 can have awidth, typically between about 0.08 and 1.0 mm, preferably between about0.08 and 0.8 mm. The membrane 23 formed at the base of the groove cutcan have a thickness such that the ratio of the membrane 23 thickness tothe thickness of the downwardly extending wall 26 immediately adjacentgroove 210 is between about 1:10 and 1:2, preferably between about 1:5to 1:2. In such embodiment the rupturable membrane 23 thickness maytypically be between about 0.08 and 0.25 mm, desirably between about 0.1and 0.2 mm.

It should also be appreciated that while polyetherurethane or nylon 66are preferred materials for insulating disk 20 and integral rupturablemembrane portion 23, other materials, preferably alkaline resistant,durable plastic material such as polysulfone, polypropylene or talcfilled polypropylene is also suitable. The combination of membrane 23thickness and aperture 48 size may be adjusted depending on the ultimatetensile strength of the material employed and level of gas pressure atwhich rupture is intended. It has been determined to be adequate toemploy only one aperture 48 and corresponding one rupturable membrane23. However, downwardly extending wall 45 in metal support disk 40 maybe provided with a plurality of comparably sized apertures with one ormore abutting underlying rupturable membrane portions 23. Preferably,two diametrically opposed apertures 48 in metal surface 45 can beemployed as shown in FIG. 4. This would provide additional assurancethat membrane rupture and venting would occur at the desired gaspressure.

The following is a description of representative chemical composition ofanode 140, cathode 120 and separator 130 for an alkaline cell 10 whichmay employed irrespective of cell size. The following chemicalcompositions are representative basic compositions for use in cellshaving the end cap assembly 14 of the present invention, and as such arenot intended to be limiting.

In the above described embodiments a representative cathode 120 cancomprise manganese dioxide, graphite and aqueous alkaline electrolyte;the anode 140 can comprise zinc and aqueous alkaline electrolyte. Theaqueous electrolyte comprises a conventional mixture of KOH, zinc oxide,and gelling agent. The anode material 140 can be in the form of a gelledmixture containing mercury free (zero-added mercury) zinc alloy powder.That is, the cell can have a total mercury content less than about 50parts per million parts of total cell weight, preferably less than 20parts per million parts of total cell weight. The cell also preferablydoes not contain any added amounts of lead and thus is essentiallylead-free, that is, the total lead content is less than 30 ppm,desirably less than 15 ppm of the total metal content of the anode. Suchmixtures can typically contain aqueous KOH electrolyte solution, agelling agent (e.g., an acrylic acid copolymer available under thetradename CARBOPOL C940 from B.F. Goodrich), and surfactants (e.g.,organic phosphate ester-based surfactants available under the tradenameGAFAC RA600 from Rhône Poulenc). Such a mixture is given only as anillustrative example and is not intended to restrict the presentinvention. Other representative gelling agents for zinc anodes aredisclosed in U.S. Pat. No. 4,563,404.

The cathode 110 can desirably have the following composition: 87-93 wt %of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 2-6wt % (total) of graphite, 5-7 wt % of a 7-10 Normal aqueous KOH solutionhaving a KOH concentration of about 30-40 wt %; and 0.1 to 0.5 wt % ofan optional polyethylene binder. The electrolytic manganese dioxidetypically has an average particle size between about 1 and 100 micron,desirably between about 20 and 60 micron. The graphite is typically inthe form of natural, or expanded graphite or mixtures thereof. Thegraphite can also comprise graphitic carbon nanofibers alone or inadmixture with natural or expanded graphite. Such cathode mixtures areintended to be illustrative and are not intended to restrict thisinvention.

The anode material 150 comprises: Zinc alloy powder 62 to 69 wt % (99.9wt % zinc containing 200 to 500 ppm indium as alloy and platedmaterial), an aqueous KOH solution comprising 38 wt % KOH and about 2 wt% ZnO; a cross-linked acrylic acid polymer gelling agent availablecommercially under the tradename “CARBOPOL C940” from B.F. Goodrich(e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrile grafted onto astarch backbone commercially available commercially under the tradename“Waterlock A-221” from Grain Processing Co. (between 0.01 and 0.5 wt.%); dionyl phenol phosphate ester surfactant available commerciallyunder the tradename “RM-510” from Rhone-Poulenc (50 ppm). The zinc alloyaverage particle size is desirably between about 30 and 350 micron. Thebulk density of the zinc in the anode (anode porosity) is between about1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent byvolume of the aqueous electrolyte solution in the anode is preferablybetween about 69.2 and 75.5 percent by volume of the anode. The cell canbe balanced in the conventional manner so that the mAmp-hr capacity ofMnO₂ (based on 308 mAmp-hr per gram MnO₂) divided by the mAmp-hrcapacity of zinc alloy (based on 820 mAmp-hr per gram zinc alloy) isabout 1.

The separator 130 can be a conventional ion porous separator consistingof cellulosic material. Separator may have an inner layer of a nonwovenmaterial of cellulosic and polyvinylalcohol fibers and an outer layer ofcellophane. Such a material is only illustrative and is not intended torestrict this invention. Current collector 80 is brass, preferably tinplated or indium plated brass to help suppress gassing.

Although the present invention has been described with respect tospecific embodiments, it should be appreciated that variations arepossible within the concept of the invention. Accordingly, the inventionis not intended to be limited to the specific embodiments describedherein but its scope is defined by the claims and equivalents thereof.

1. An electrochemical cell comprising a housing having an open end anopposing closed end and side wall therebetween and an insulating sealingplug inserted into the open end of said housing closing said open end,said cell having a positive and a negative terminal and an aqueousalkaline electrolyte, said insulating sealing plug comprising anelastomeric thermoplastic polymeric material.
 2. The cell of claim 1wherein said polymeric material has an ultimate percent elongationgreater than about 200 percent.
 3. The cell of claim 1 wherein saidpolymeric material has an ultimate percent elongation greater than about300 percent.
 4. An electrochemical cell comprising a housing having anopen end an opposing closed end and side wall therebetween and aninsulating sealing plug inserted into the open end of said housingclosing said open end, said cell having a positive and a negativeterminal and an aqueous alkaline electrolyte, said insulating sealingplug comprising polyetherurethane material.
 5. The cell of claim 4wherein said insulating sealing plug comprisespolytetramethyleneetherurethane material.
 6. An electrochemical cellcomprising a housing having an open end an opposing closed end and sidewall therebetween and an end cap assembly inserted into the open end ofsaid housing closing said housing, said cell having a positive and anegative terminal and an aqueous alkaline electrolyte, said end capassembly comprising an electrically insulating sealing plug, saidinsulating sealing plug comprising polyetherurethane material and havingan elongated electrically conductive current collector passingtherethrough, the current collector being in electrical contact with acell terminal.
 7. The cell of claim 6 wherein said housing iscylindrical.
 8. The cell of claim 7 wherein said housing has a surfacefacing the cell interior and said insulating sealing plug comprises aperipheral edge abutting a portion of said housing surface and there isno seal coating applied between the peripheral edge of said insulatingplug and said housing surface.
 9. The cell of claim 6 wherein saidpolyetherurethane is an elastomeric thermoplastic material.
 10. The cellof claim 9 wherein said polyetherurethane material has an ultimatetensile strength less than the ultimate tensile strength of nylon 66 andan ultimate elongation of greater than 200 percent.
 11. The cell ofclaim 6 wherein said insulating sealing plug comprises apolytetramethyleneetherurethane material.
 12. The cell of claim 11wherein said polytetramethyleneetherurethane material is formed from thereaction product of a polytetramethyleneglycol and a diisocyanate. 13.The cell of claim 6 wherein said insulating sealing plug comprising athinned portion integrally formed therein, said thinned portion forminga rupturable membrane which ruptures when gas pressure within the cellrises, wherein said rupturable membrane comprises a polyetherurethanematerial.
 14. The cell of claim 13 wherein said thinned portion formingsaid rupturable membrane comprises a polytetramethyleneetherurethanematerial.
 15. In an electrochemical cell comprising a cylindricalhousing having an open end an opposing closed end and side walltherebetween and an end cap assembly inserted into the open end of saidhousing closing said housing, said cell having a positive and a negativeterminal and an aqueous alkaline electrolyte, said end cap assemblycomprising an electrically insulating sealing disk, said insulatingsealing disk having an elongated electrically conductive currentcollector passing therethrough, the current collector being inelectrical contact with a cell terminal, the improvement comprising:said insulating sealing disk comprising polyetherurethane material. 16.The cell of claim 15 wherein said polyetherurethane is an elastomericthermoplastic material.
 17. The cell of claim 16 wherein saidpolyetherurethane material has an ultimate tensile strength less thanthe ultimate tensile strength of nylon 66 and an ultimate elongation ofgreater than 200 percent.
 18. The cell of claim 15 wherein saidinsulating sealing disk comprises a polytetramethyleneetherurethanematerial.
 19. The cell of claim 18 wherein saidpolytetramethyleneetherurethane material is formed from the reactionproduct of a polytetramethyleneglycol and a diisocyanate.
 20. The cellof claim 15 wherein said insulating sealing disk comprising a thinnedportion integrally formed therein, said thinned portion forming arupturable membrane which ruptures when gas pressure within the cellrises, wherein said rupturable membrane comprises a polyetherurethanematerial.
 21. The cell of claim 20 wherein said thinned portion formingsaid rupturable membrane comprises a polytetramethyleneetherurethanematerial.
 22. The cell of claim 15, the improvement further comprising:the end cap assembly comprising said insulating sealing disk, a supportdisk comprising metal overlying said insulating sealing disk, and an endcap comprising metal overlying said metal support disk, and an elongatedcurrent collector in electrical contact with said end cap, when the cellis viewed in vertical position with the end cap assembly on top, whereinsaid insulating sealing disk electrically insulates the support disk andend cap from the cell housing; wherein said housing has an edge at theopen end thereof and said insulating sealing disk, metal support disk,and end cap each have a peripheral edge; wherein said support disk is ofsingle piece metallic construction having at least one aperturetherethrough; wherein the edge of said housing at the open end thereofis crimped over the peripheral edge of said insulating sealing disklocking said insulating sealing disk in place within said housing;wherein the peripheral edge of the insulating sealing disk is crimpedover the peripheral edge of both said end cap and the peripheral edge ofsaid metal support disk thereby locking said metal support disk and saidend cap in place within the said insulating sealing disk; wherein saidinsulating sealing disk has a portion of its surface underlying saidaperture in said support disk when the cell is viewed in verticalposition with the end cap assembly on top, said portion of saidinsulating disk underlying said aperture having a groove on a side ofits surface facing the cell interior, said groove having an open end andopposing closed base wherein the base of said groove forms a thinnedrupturable membrane abutting said aperture in said support disk, wherebywhen gas pressure within the cell rises, said rupturable membranepenetrates through said aperture in said metal support disk and rupturesthereby releasing gas from the cell interior through said aperture. 23.The cell of claim 15 wherein the end cap is in juxtaposed and spacedapart relationship with said membrane thereby providing spacetherebetween into which space said membrane can rupture.
 24. The cell ofclaim 23 wherein said end cap comprises at least one vent aperturetherethrough so that when said membrane ruptures, gas from within thecell can pass into said space between the end cap and the membrane andthen through said vent aperture and out to the external environment. 25.The cell of claim 15 wherein said groove on said insulating disk surfacecircumvents the center of said sealing disk.
 26. The cell of claim 15wherein said rupturable membrane formed by said groove has a width tothickness ratio of between about 2.5 to 1 and 12.5 to
 1. 27. The cell ofclaim 26 wherein the rupturable membrane at the based of said groove hasa thickness of between about 0.08 and 0.25 mm.
 28. The cell of claim 15wherein the housing comprises steel and said housing has a wallthickness between 4 and 12 mils (0.10 and 0.30 mm).
 29. The cell ofclaim 15 wherein a portion of the insulating disk contacts said supportdisk in the region of a surface of said support disk immediatelyadjacent said aperture.
 30. The cell of claim 15 wherein the metalsupport disk has a central aperture located at the center of saidsupport disk and at least a portion of the elongated current collectorpasses through said central aperture and the head of said currentcollector is welded to said end cap.
 31. The cell of claim 15 whereinsaid insulating sealing disk comprises a plastic material having adownwardly extending surface slanted at an angle less than 90 degreesfrom the cell's central longitudinal axis and not parallel to saidlongitudinal axis, said downwardly extending surface of said insulatingdisk extends downwardly from a high point thereon to low point thereon,said high point being closer to the cell's central longitudinal axisthan said low point when the cell is viewed in vertical position withthe end cap assembly on top, wherein said support disk has a downwardlyextending surface slanted at an angle less than 90 degrees from thecell's central longitudinal axis and not parallel to said longitudinalaxis, said downwardly extending surface of the support disk extendsdownwardly from a high point thereon to low point thereon, said highpoint being closer to the cell's central longitudinal axis than said lowpoint when the cell is viewed in vertical position with the end capassembly on top, wherein the downwardly extending surface of theinsulating disk underlies and abuts at least a substantial portion ofthe downwardly extending surface of said support disk, wherein said atleast one aperture penetrates through said downwardly extending surfaceof said support disk, wherein a portion of said rupturable membraneunderlies and abuts said aperture.
 32. The cell of claim 31 wherein thedownwardly slanted surface of said insulating sealing disk is slanted atan angle of between about 35 and 80 degrees from the cell's centrallongitudinal axis.
 33. The cell of claim 32 wherein said downwardlyextending surface of said support disk is slanted from the cell'scentral longitudinal axis at the same angle as said downwardly extendingsurface of the insulating sealing disk.
 34. The cell of claim 32 whereinthe average space between the downwardly extending surface of said metalsupport disk and said underlying and abutting downwardly extendingsurface of said insulating sealing disk is no more than about 0.5 mm.35. The cell of claim 32 wherein the average space between thedownwardly extending surface of said metal support disk and saidunderlying and abutting downwardly extending surface of said insulatingsealing disk is between about 0.1 and 0.5 mm.
 36. The cell of claim 15wherein said aperture in said support has an area between about 2.5 and16 mm and said rupturable membrane at the base of said groove has athickness between about 0.08 and 0.25 mm.
 37. The cell of claim 15wherein the end cap assembly does not include an insulating washerbetween said end cap and said metal support disk.
 38. The cell of claim15 wherein support disk has a pair of opposing apertures in thedownwardly extending surface of said disk.
 39. The cell of claim 31wherein the support disk has a peripheral outer edge and a substantiallyflat central portion with a central aperture through said centralportion, wherein said central portion is at right angle to the cell'scentral longitudinal axis and said downwardly extending surface of thesupport disk extends downwardly from said central portion to saidperipheral outer edge.
 40. The cell of claim 39 wherein the peripheraledge of said support disk and the peripheral edge of said end cap biteinto the peripheral edge of said insulating sealing disk and exertradial compressive forces on said sealing disk.
 41. The cell of claim 15wherein said housing has a surface facing the cell interior, whereinsaid insulating sealing disk comprises a peripheral edge abutting aportion of said housing surface and there is no seal coating appliedbetween the peripheral edge of said insulating disk and said housingsurface.
 42. The cell of claim 15 wherein the cell is an AAA size cell.43. The cell of claim 15 wherein the cell is an AA size cell.